Java Program to Determine Number of Bytes Written to File using DataOutputStream

Last Updated : 23 Jul, 2025

The Java OutputStream class, java.io.OutputStream, is the base class of all output streams in the Java IO API. An output stream accepts output bytes and sends them to some sink. Applications that need to define a subclass of OutputStream must always provide at least a method that writes one byte of output.

To get the number of bytes written we firstly create an object of FileOutputStream by passing the file's path that is shown in code below as FileOS.
Then we create an object of DataOutputStream by passing the FileOS i.e. object of FileOutputStream that is shown in code below as DataOS.
Now, we will inject text into this text file by using writeBytes() method of DataOutputStream. To get the size of bytes written we use size method of DataOutputStream Class on the object DataOS.

Program 1:

Java

// Java program to determine number of bytes
// written to DataOutputStream

import java.io.*;

public class NumberOfBytesInOutputStream {
    public static void main(String[] args)
    {
        try {
          
            // creates object of FileOutputStream by passing
            // file Bytes.txt
            FileOutputStream FileOS
                = new FileOutputStream("C:/Bytes.txt");

            // creates object of DataOutputStream by
            // passing object of FileOutputStream i.e.
            // FileOS
            DataOutputStream DataOS = new DataOutputStream(FileOS);

            // writes the string passed to object of
            // DataOutputStream
            DataOS.writeBytes(
                 "GeeksforGeeks is the best place to learn Coding online.");

            // Stores the number of bytes to total_bytes
            // variable using size() method of
            // DataOutputStream class
            int total_bytes = DataOS.size();

            // Showing the number of bytes as output in
            // console
            DataOS.close();

            System.out.println("Total " + total_bytes
                        + " bytes were written to stream.");
        }
        catch (Exception e) 
        {
            System.out.println("Exception: " + e.toString());
        }
    }
}

Output:

Program 2:

Java

// Java program to determine number of bytes
// written to DataOutputStream

import java.io.*;

public class NumberOfBytesInOutputStream2 {
    public static void main(String[] args)
    {
        try {
          
            // creates object of FileOutputStream by passing
            // file Bytes.txt
            FileOutputStream FileOS = new FileOutputStream("C:/NumberOfBytes.txt");

            // creates object of DataOutputStream by passing
            // object of FileOutputStream i.e. FileOS
            DataOutputStream DataOS = new DataOutputStream(FileOS);

            // create string S with the desired text
            String S = "GeeksforGeeks article is best for getting cs concepts.";

            // writes the string passed to object of
            // DataOutputStream
            DataOS.writeBytes(S);

            // Stores the number of bytes to total_bytes
            // variable using size() method of
            // DataOutputStream class
            int total_bytes = DataOS.size();

            // Showing the number of bytes as output in
            // console
            System.out.println("Total " + total_bytes
                      + " bytes were written to stream.");

            DataOS.close();
          
        }
        catch (Exception e) 
        {
            System.out.println("Exception: " + e.toString());
        }
    }
}